In any camera system, range to the object may be approximated for objects closer than the hyperfocal distance by observing the sharpness of focus of the image of the object (or a portion thereof) as the camera lens is moved or indexed across its focusing range. At the position of sharpest focus the range of the object (or portion thereof) may be read directly from a calibrated focus adjustment. This can be done whenever there is sufficient detail on the object surface or at its boundary to permit the focusing to be readily apparent to the human eye or to a processor which can determine sharpness of focus based upon fine detail. Sharpness of focus is determined when the spatial high frequency content of a region is maximized or when the percentage modulation at a region is maximized, or both. This can be achieved by many well known digital processing schemes which use the digitized output from a TV camera as input or alternatively, by the use of instantaneous Fourier transform techniques which instantly yield spatial frequency information. However, both techniques fail when the object has insufficient surface detail or its edges are gently curving so as to defy the requirements for the presence of some innate structure upon which to judge proper focusing.
Projecting a pattern with detail on the surface can enable acquiring the desired surface measurements. However, if sequential processing of the image is employed, the time required may be greater than allowable for a particular system function. The present invention proposes to enable rapid image evaluation by parallel detector readout and optical processing.